The industrially most important known per salts are sodium percarbonate and sodium perborate which are employed in washing agents.
While sodium percarbonate is readily soluble but not very storage stabile, the reverse for sodium perborate (hereinafter unless otherwise indicated there is always understood the tetrahydrate) which is very difficultly soluble but instead is substantially safer to store. Also sodium perborate is more abrasion resistant than sodium percarbonate.
In order for the sodium percarbonate to approach the storage stabiliy and abrasion resistance of sodium perborate there have already been many proposals.
Thus silica in the form of sodium silicate was added to the sodium percarbonate which was formed both from solid soda and more preferably from aqueous soda solutions by reaction with hydrogen peroxide, see British Pat. No. 174,891.
However, the stability was not substantially improved by the simple mixing.
Also the use of a fluidized bed which consists of soda particles on which aqueous hydrogen peroxide was sprayed was not successful, see French Pat. No. 2,076,430.
Therefore, the art has already gone to producing sodium percarbonate by spraying a sodium percarbonate suspension or solutions of hydrogen peroxide and soda on nuclei already present. In that case, these nuclei can consist of sodium percarbonate or also of another per salt, as e.g. sodium perborate.
However, this process has prove to be difficult to carry out industrially since either a premature crystallization takes place in the injection nozzle or an inhomogeneous product is formed according to German OS 2,060,971.
By the impregnation of the percarbonate nuclei with the two aqueous solutions of hydrogen peroxide and sodium carbonate before introduction into a fluidized bed dryer to be sure homogeneous particles are formed, but besides other constituted technical difficulties in the carrying out of this process, the thus obtained percarbonate particles also were not stabile enough, see German OS 2,250,720.
To be sure these disadvantages are supposed to be overcome by the process of German OS 2,733,935 in which namely a condensed phosphate of an alkali metal, such as e.g., sodium hexametaphosphate is present during the impregnation of the nuclei, which then themselves are freed from water in a fluidized bed dryer, but the simultaneous addition of this sodium percarbonate together with sodium perborate in a washing agent mixture requires first the production of the sodium percarbonate according to German OS 2,733,935 and additionally the separate production of sodium perborate according to known processes.
Thus previously there must always be carried out two separate processes of production if two materials are to be introduced into a washing agent either separately or as a common product, e.g. according to German OS 2,060,971.
The object of the application therefore is the development of a process according to which a per salt is producible in a single step which is more readily soluble than sodium perborate and has a higher active oxygen content than this.